The hip joint is a synovial joint, joining the pelvis to the proximal portion of the femoral bone. Synovial joints are the most common types of joints in mammals, and are typical of nearly all limb joints. The contacting surfaces of said the pelvic, the acetabulum, and the contacting surface of the femoral bone, the caput femur, are smooth and rounded, and covered by articular cartilage. A synovial membrane, encapsulates the joint, forming a hip joint cavity, which contains synovial fluid. Outside the synovial membrane is a fibrous capsule and ligaments, forming an articular capsule.
There are both natural and pathological processes leading to deteriorated joint function. With age and wear, the articular cartilage becomes less effective as a shock absorber and a lubricated surface. Different degenerative joint diseases, such as arthritis, osteoartrithis, or osteoarthrosis, accelerate the deterioration.
Hip joint Osteoarthritis is a syndrome in which low-grade inflammation result in pain in the hip joints, caused by abnormal wearing of the Cartilage that act as a cushion inside if the hip joint. This abnormal wearing of the cartilage also results in a decrease of the joints lubricating fluid called Synovial fluid. Hip joint Osteoarthritis is estimated to affect 80% of all people over 65 years of age, in more or less serious forms.
The present treatment for hip osteoarthritis comprises NSAID drugs, local injections of Hyaluronic acid or Glucocorticoid to help lubricating the hip joint, and replacing part of the hip joint with a prosthesis through hip joint surgery.
The replacing of parts of the hip joint is one of the most common surgeries to date performed at hundreds of thousands of patients in the world every year. The most common method comprises placing a metal prosthesis in Femur and a plastic bowl in Acetabulum. This operation is done through an incision in the hip and upper thigh and through Fascia Iata and the lateral muscles of the thigh. To get access to the joint, the supporting Capsule attached to Femur and Ilium needs to be penetrated, making it difficult to get a fully functional joint after the surgery. Femur is then cut at the neck with a bone saw and the prosthesis is placed in femur either with bone cement or without. Acetabulum is slightly enlarged using an Acetabular reamer, and the plastic bowl is positioned using screws or bone cement.
The complications after hip joint surgery includes dislocation of the hip joint and loosening of the prosthesis from its fixation in the femoral bone. The loosening and/or dislocation of the prosthesis could be induced by an abnormal strain being placed on the hip joint from e.g. the patient falling or making a rapid movement of the hip, or by a bodily macrophage reaction.